Manufacturing method of an electronic device including overmolded mems devices

ABSTRACT

A method manufactures an electronic device comprising a MEMS device overmolded in a protective casing. The MEMS device includes an active surface wherein a portion of the MEMS device is integrated, and is sensitive, through a membrane, to chemical/physical variations of a fluid. Prior to the molding step, at least one resin layer is formed on at least one region overlying the active surface in correspondence with the membrane. After, at least one portion of at least one resin layer is removed from at least one region, so that in the region an opening is formed, through which the MEMS device is activated from the outside of the protective casing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119(a) of ItalianPatent Application No. MI2007A 002099, filed Oct. 30, 2007, whichapplication is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a method for manufacturing anelectronic device comprising overmolded MEMS devices.

The invention also relates to an electronic device comprising overmoldedMEMS devices.

The invention particularly, but not exclusively, relates to a method formanufacturing an electronic device comprising MEMS sensors mounted on anLGA substrate, wherein the MEMS sensor needs a physical interface tocommunicate with the outside of the electronic device and the followingdescription is made with reference to this field of application by wayof illustration only.

2. Description of the Related Art

As it is well known, a MEMS device (micro-electro-mechanical system) isa miniaturized device or, in any case, a device having micrometric sizewhich integrates mechanical and electrical functions in a chip or die ofsemiconductor material, for example of silicon, and which is realized byusing micro-manufacturing lithographic techniques. The final assembleddevice is typically made of the silicon die wherein the MEMS device isintegrated and, optionally, of integrated circuits for specificapplications mounted on a substrate, for example of the LGA or BGA type(Land Grid Array or Ball Grid Array), flanked to or piled onto the MEMSdevice, by using conventional assembling processes.

A cover or cap, fixed to the substrate, overmolds the MEMS device andthe other devices mounted on the substrate, forming a casing whichprotects the MEMS device against external physical stresses.

If the MEMS device is a pressure, gas, liquid sensor or a microphone,the cover is provided with a window to allow the interaction between thedevice and the outside of the assembled device.

It is also known that the substrate of the LGA/BGA type is formed byconductive layers insulated from each other by means of layers ofinsulating or dielectric material. The conductive layers are shaped inconductive tracks insulated from each other by layers of insulating ordielectric material. Conductive through-holes, called “vias”, typicallyrealized through the insulating layers according to an orthogonalorientation with respect to the insulating layers, are provided to formconductive paths between conductive tracks belonging to differentconductive layers.

The MEMS devices are then electrically connected with the outside of thefinal device through wires connecting contact pads provided on the MEMSdevices with conductive tracks present on the substrate inside thecover.

A solution of this type is described for example in the PCT patentapplication, with publication number WO 2007/042336, filed on Apr. 26,2006 by the assignee of the present application. In this patentapplication a MEMS device, in particular a pressure sensor, is realizedon a substrate of the LGA type, to which it is glued, through a layer ofepoxy glue. This sensor has a cavity above which there is a membrane andis connected to the substrate through metallic conductive wires. It isthen covered by a closing wafer equipped with an opening incorrespondence with the membrane of the sensor and through which thesensor is in communication with the outside. All the device is finallyovermolded in a casing.

Although advantageous under several aspects, this solution showsdifferent drawbacks. In fact, the complete device is made by firstrealizing a casing bottom, then the different components are affixed tothe casing bottom, and finally the casing is molded and the element tocontrol the sensor is inserted through the window of the casing. Forthese devices, moreover, the procedure of alignment and positioning ofthe window to introduce the element for controlling the sensor is rathercomplicated, making the realization of the device difficult to bereproduced. Moreover, the manufacturing process of these devices iscomplicated by the presence of different assembling steps and relativelyexpensive.

A second solution, described in U.S. Patent Application Publication No.2002/0070464 to the assignee of the present application, provides theuse of a casing which, by using a conventional technique, is equippedwith a window in correspondence with an integrated electronic device,for example a sensor housed inside the casing and which must be put incommunication with the outside of the casing. This window is obtained byusing the same mold which is used to realize the casing; this mold isequipped with a protrusion projecting internally in correspondence withthe sensor. After having fixed the sensor and a relative controlcircuitry to a semiconductor substrate, which serves as support, asurface of the sensor is covered with a coating layer formed by materialof the elastic type. The substrate is inserted in the mold so that theprotrusion is in correspondence and in contact with the coating layer.The mold is then filled in by injection with an insulating material torealize, in a single step, the casing with window.

Although meeting the aim, also this solution is not exempt fromdrawbacks, such as the reproducibility of the process, the stability ofthe shape of the dispensed elastic material, the reliability and thestrength of the device which can, in fact, be subject to delaminationsat the interface between the insulating material and the material of theelastic type.

Another technique for manufacturing a MEMS device overmolded in a casinguses a molding machine commercially known as “film assisted mold,” whichrealizes the cap of the device thanks to a polymeric film, interposedbetween the mold and the device itself, which allows to expose thesilicon in a remarkably controlled way.

The disadvantage of this solution consists in that the increase of thesize of the holes made on the cap determines a weakening of the siliconslice which serves as cap, and a subsequent breakage of this one duringthe completion of the device.

Moreover, to ease the interaction between a MEMS device, for example apressure sensor, and the fluid outside the casing overmolding it methodshave been implemented for manufacturing micro-channels buried in theMEMS device, below the membrane or active element. A method whichrealizes buried micro-channels of this type is described in the patentapplication, with publication number US 2006/0260408, filed on May 4,2006 by the assignee of the present application.

A second method known for the formation of micro-channels is describedin the US Patent Application Publication No. 2006/0246416. According tothis method, the micro-channels are formed in the substrate of a first“chip”, called micro-porous “chip”, which is then glued to a second“chip”, called micro-fluidic “chip”. A third example of formation ofmicro-channels is described in the US Patent Application Publication No.2005/0151244, wherein micro-channels are formed first in a “coolingplate” using to cool an electronic “chip”.

It is known to realize micro-channels in a silicon substrate through thecombination of suitably shaped layers.

Another aspect to be taken into account in the manufacturing of the MEMSdevices, in particular in the ultra thin ones, or for “package”applications, is the use of photo-sensitive resins (“photo-resist”)being very thick and with high “aspect ratio” (i.e.: with high ratiobetween width and height of the device, also known as “aspect ratio”),so as to obtain vertical walls in relatively high structures with a goodcontrol of the size on the whole height.

A known technique to obtain structures with high “aspect ratio” withsub-micron resolution in very thick “photo-resist” is the X-raylithography, used in the LIGA process (“Lithography, Galvanoforming andAbformung”) to form very thick layers of PMMA (polymethylmethacrylate).However, the cost of the manufacturing of a device, made by using theLIGA process with X-ray lithography, is strongly influenced by the highcost of the X-ray source (synchrotron radiation) and by the complextechnology of the masks.

Recently, instead, a new type of “photo-resist”, having characteristicssimilar to the PMMA and having the possibility of being used in aprocess of the LIGA type, is used for the applications of ultrathin MEMSwith high “aspect ratio”.

The characteristics of this new type of “photo-resist”, called SU-8, aredescribed in the publications “A Novel Fabrication Method of EmbeddedMicro Channels Employing Simple UV Dosage Control and AntireflectionCoating”, F. G. Tseng, Y. J. Chuang and W. K. Lin, 2002 IEEE; and“High-Aspect-Ratio, Ultrathick, Negative-Tone Near-UV Photoresist forMEMS Applications,” M. Despont, H. Lorenz, N. Fahrni, J. Brugger, P.Renaud and P. Vettiger, 1997 IEEE.

The SU-8 is a “photo-resist” similar to the epoxy resin, sensitive tothe radiation near the UV and based onto the resin EPON SU-8 (from“Shell Chemical”). The fundamental characteristic, which makes the SU-8useful for the ultrathick “photo-resist” applications, is its very lowoptical absorption in a range of radiations near the UV, whichdetermines uniform exposure conditions according to the thickness,allows to form perfectly vertical walls and to have a good size controlon the height of the whole formed structure. Another advantage of theSU-8 is its capacity of self-planarization during the “prebake” and thento eliminate the “edge-bead” effect, determining a good contact betweenthe mask and the “photo-resist” in the contact lithography.

As reported in the second one of the above publications, it has beenproved that, with a coating having single SU-8 layer, thicknesses can beobtained, in a reproducible way, of more than 500 mm and that eventhicker “photo-resist” can be obtained through multiple coatings, up to1200 mm of thickness with a double-layer coating. The “aspect ratio”found for structures exposed to the radiation near the UV (400 nm) canbe greater than 18 and remains constant for a thickness comprisedbetween 80 and 1200 mm.

BRIEF SUMMARY

One embodiment is a device comprising overmolded MEMS devices, havingsuch structural and functional characteristics as to allow therealization of this electronic device with low-cost manufacturingprocesses overcoming the limits and/or the drawbacks still affecting theelectronic devices realized according to the prior art.

One embodiment is a method for manufacturing an electronic devicecomprising overmolding MEMS devices, wherein the opening putting theMEMS device in communication with the outside is realized throughphotolithography with “photo-resist” thick layers, for example of thetype known as SU-8.

One embodiment is a method for manufacturing an electronic device whichcomprises a MEMS device overmolded in a protective casing, the MEMSdevice comprising an active surface wherein a portion of said MEMSdevice is integrated, said MEMS device being sensitive, through amembrane, to chemical/physical variations of a fluid.

The method comprises the steps of:

-   -   forming, prior to the molding step, at least one photo-resist        resin layer on at least one central region overlying said active        surface in correspondence with said membrane;    -   removing at least one portion of said at least one resin layer        from said at least one central region, so that in said region an        opening is formed, through which the MEMS device is activated        from the outside of said protective casing.

One embodiment is an electronic device which comprises a MEMS deviceovermolded in a protective casing, said MEMS device comprising an activesurface wherein a portion of said MEMS device is integrated, said MEMSdevice being sensitive through a membrane, to chemical/physicalvariations of a fluid. The MEMS device is activated from the outside ofsaid protective casing through an opening placed between at least onefirst and at least one second resin layer, in correspondence with saidmembrane. The characteristics and the advantages of the method and ofthe device will be apparent from the following description of theirrespective embodiments given by way of indicative and non-limitingexample with reference to the annexed drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In these drawings:

FIGS. 1A, 1B show the steps of a first implementation example of themanufacturing method of a first embodiment of the electronic devicecomprising MEMS devices;

FIG. 2 shows a TEM image (Transmitted Electronic Microscopy) from aboveof the first embodiment of the electronic device of FIG. 1 comprisingMEMS devices;

FIGS. 3A-3C show the steps of a second implementation example of themanufacturing method of a second embodiment of the electronic devicecomprising MEMS devices;

FIGS. 4A-4E show an application of the steps of the secondimplementation example of the manufacturing method of a secondembodiment of the electronic device comprising MEMS devices;

FIGS. 5A, 5B show the TEM images of two portions of the device obtainedwith this implementation example of the method;

FIG. 6 shows a section of an electronic device realized with the method;and

FIG. 7 shows a three-dimensional view of the buried micro-channels,realized with the method.

DETAILED DESCRIPTION

With reference to FIGS. 1A and 1B, the steps are shown of a firstimplementation example of the manufacturing method of a first embodimentof the electronic device comprising a MEMS device.

Hereafter in the description it will be apparent that the method can beimplemented to obtain indifferently a first or a second embodiment of anelectronic device incorporating MEMS devices.

In the following description it is also taken for granted that the MEMSdevice has already been realized above a semiconductor substrate of theelectronic device housing it.

FIG. 1A shows a first implementation step of the method which providesthe formation of a photo-resist resin layer above the MEMS devicecomprised in the electronic device and the successive partial removal ofthis resin layer prior to the overmolding of the device in a protectivecasing.

In particular, a substrate 12 has been shown, for example of the LGA/BGAtype comprising an insulating core of a polymeric material (for exampletriazine and bismaleimide resin (BT)) and coated by metallic layers, forexample of copper, wherein, according to conventional techniques,conductive tracks are shaped, not shown in the figure. Above thesubstrate 12 a MEMS device 13 is glued serving as sensor, i.e., it issensitive to chemical and/or physical variations of a fluid presentoutside the electronic device. The MEMS device 13 is integrated in adie, for example of silicon, and has a non-active surface 14 and anactive surface 15, opposed to the non-active surface 14, below which acavity 16 is present. Above the cavity 16 there is a membrane 17 havinga top surface that is part of the active surface 15.

Advantageously, on the whole surface 15 of the MEMS sensor 13 aphoto-resist resin layer 21 is deposited, for example of the SU-8 type,through the “spin coating” technique.

The fundamental characteristic, which makes the SU-8 useful for theultrathick “photo-resist” applications, is its very low opticalabsorption in a range of radiations near the UV, which determinesuniform exposure conditions according to the thickness, allows to formperfectly vertical walls and to have a good size control on the heightof the whole formed structure. Another advantage of the SU-8 is itscapacity of self-planarization.

Advantageously, the resin layer 21 deposited has a relatively highthickness greater than 20 μm.

Advantageously, the resin layer 21 deposited has a greater thicknessthan the maximum height of the metallic wires 18, which is equal to 150micrometers.

Subsequently, the resin layer 21 is exposed to a radiation near in thespectrum to UV radiation and an etching of the chemical type or the“ashing” technique, to remove the excess resin layer from a centralregion 19, overlying the surface 15 in correspondence with the membrane17, and from a peripheral region 20 overlying a peripheral portion ofthe surface 15. This peripheral region 20, is, in fact, apt to housemetallic wires 18 serving as electric connections between the MEMSsensor 13 and the substrate 12, which has suitable pads, not shown inthe figure, which are connected to the conductive tracks through theseconductive wires 18.

Finally, a first and a second portion of the resin layer 21 are left incorrespondence with regions 22 overlying the active surface 15 andadjacent to the central region 19, so that an opening 23 is formed incorrespondence with the central region 19, which allows the interactionof the sensor 13, through the membrane 17, with an external fluid.

Advantageously, in one embodiment the resin layer is deposited by meansof the known technique of “screen printing”.

Advantageously, in one embodiment the resin layer is deposited by meansof the known technique of “dispensing”.

Subsequently, as shown in FIG. 1B a molding step of a protective casing(“molding”) is carried out, through conventional techniques. Anelectronic device 10 is thus formed which, in the end, includes the MEMSdevice 13 overmolded inside a protective casing or “package” 24. Inparticular, the protective casing 24 comprises the MEMS device 13,overlaid by the two residual portions of the resin layer 21, theelectric connections 18 and the substrate 12, leaving the opening 23exposed in correspondence with the membrane 17 of the MEMS device 13.

FIG. 2 shows a TEM image from above of the electronic device 10.

With reference to FIGS. 3A-3C, the steps are shown of a secondimplementation example of the manufacturing method leading to a secondembodiment of the electronic device comprising MEMS devices. This secondimplementation example provides the formation of the resin layer on aportion of the MEMS device in correspondence with the active membraneand the successive removal of this resin layer after the overmolding ofthe device in a protective casing.

FIG. 3A shows a first step of the second implementation example of themethod. On a substrate 112 is glued a MEMS device 113 serving as sensor.The MEMS device 113 is integrated in a die, for example of silicon, andhas a nonactive surface 114 and an active surface 115 opposed to thenon-active surface 114. Below the active surface 115, there is a cavity116, above which there is a membrane 117. The MEMS sensor 113 isconnected, through conductive wires 118, to the substrate 112 which haspads, not shown in the figure, connected to the conductive tracks.

Advantageously, a photo-resist resin layer 121, for example of the SU-8type, is deposited on a region 119 overlying the active surface 115 ofthe MEMS sensor 113 in correspondence with the membrane 117, whileregions 122 overlying the active surface 115 and adjacent to the region119 are not coated by the photo-resist resin.

Advantageously, the resin layer 121 deposited has a relatively highthickness greater than 20 μm.

Advantageously, the resin layer 121 deposited has a thickness greaterthan the maximum height of the metallic conductive wires 118, which isequal to 150 micrometers.

Advantageously, according to one embodiment, the resin layer 121 isdeposited through the “spin coating” technique.

Advantageously, according to one embodiment, the resin layer 121 isdeposited through conventional photolithography.

Advantageously, according to one embodiment, the resin layer 121 isdeposited through the “screen printing” technique.

Advantageously, according to one embodiment, the resin layer isdeposited through the “dispensing” technique.

Subsequently, as shown in FIG. 3B, the molding step is carried out,through conventional “molding” techniques, in which inside a protectivecasing or “package” 124, the MEMS device 113, the electric connections118 and the substrate 112, are encompassed leaving the resin layer 121exposed in correspondence with the membrane 117 of the MEMS device 113.

Subsequently, a final cleaning step is carried out in which the resinlayer 121 is totally removed from the region 119 and, in its place, anopening 123 is formed which allows the interaction of the sensor 113with an external fluid. FIG. 3C, corresponding to this step, shows theelectronic device 110 thus obtained.

FIGS. 4A-4E show, by way of example, the steps relative to anapplication of the second implementation example of the manufacturingmethod, in case the “dispensing” technique is used for depositing theresin layer.

In particular, FIG. 4A shows the gluing step, through the known“flip-chip” technique, between a substrate 212 and a MEMS sensor 213having an active surface 215, below which there are a cavity 216 and amembrane 217 placed above the cavity 216. This gluing step is followed,as shown in FIG. 4B, by a distribution step of photo-resist resin, suchas to form an ovoidal region of resin 221 above a region 219 overlyingthe active surface 215 in correspondence with the membrane 217.

Advantageously, the photo-resist resin used to form the ovoidal region221 is of the SU-8 type.

This resin region 221 is subsequently subjected to a “curing” thermalprocess, followed by a step, shown in FIG. 4C, of electrochemicalcleaning, through “plasma cleaning” and of formation of metallicconnections 218 between the MEMS sensor 213 and the substrate 212through “wire bonding”.

FIG. 4D shows the overmolding step, through conventional “molding”techniques, inside a protective casing or “package” 224, of the MEMSdevice 213, of the electric connections 218 and of the substrate 212,leaving the resin ovoidal region 221 exposed.

A final cleaning step follows, from which the device 210 shown in FIG.4E is obtained, wherein the resin region 221 is totally removed, leavingan opening 223 in correspondence with the region 219, which allows theinteraction of the sensor 213 with an external fluid.

FIGS. 5A, 5B show two TEM images (Transmitted Electronic Microscopy) oftwo portions of the device 210. In particular, FIG. 5A shows the TEMimage of the step shown in FIG. 4C, while FIG. 5B shows the TEM imagefrom above of a stripe of the device 210.

The method has a further advantage in that it allows to realize a devicecomprising three-dimensional micro-channels which create a preferredpath for the passage of a fluid coming from the outside of the device.

FIG. 6 shows for example a section of an electronic device 310comprising buried micro-channels, realized with the first implementationexample of the method.

In particular, the device 310, which can be a pressure or gas sensordevice, comprises a monolithic silicon body 311, having a lower surface312 and an upper surface 313 and comprising a buried cavity 314 which isextended to a certain distance from the upper surface 313 and delimitswith the upper surface a flexible membrane 315.

On a first lateral region 316 of the upper surface 313 there is a firstportion of a first photo-resist resin layer 317 and on a second lateralregion 318 of the upper surface 313 there is a second portion of a firstphoto-resist resin layer 317, formed with the method described in FIGS.1A and 1B. Between the two portions of the first resin layer 317 achannel region 319 is interposed which communicates through an accessopening 320 with the buried cavity 314, forming a micro-channelstructure. On the portion of resin layer 317 overlying the lateralregion 316 there is a first portion of a second resin layer 321, whichis exactly overlapped onto the first portion of resin layer 317. On theportion of resin layer 317 overlying the lateral region 318 there is asecond portion of the second resin layer 321, which extends beyond theresist layer 317, projecting onto the channel region 319, and isseparated from the first portion of the second resin layer 321, througha space 322 communicating with the channel region 319. The portions ofthe second resin layer 321 are formed by reiterating the method of FIGS.1A and 1B. Subsequently, the “film assisted molding” is carried outleaving the first resin layer 317 exposed.

The device 310 is overmolded, together with the portions of the firstand of the second resin layer 317 and 321, in a protective casing or“package” 323 which has an opening 324 in correspondence with the space322, through which a fluid present outside the package 324 penetratesinside the channel region 319.

The micro-channels are realized by using a standard photo-lithography.With at least two resin layers a complex structure withthree-dimensional channels is realized, like the one shown in FIG. 7.

In conclusion, the method allows to realize economic pressure sensorswith other “aspect ratios”.

With the method it is also possible to realize on the chip a preferredpath for gases or liquids flowing inside the package up to the sensor.This method, in fact, can be applied to gas, pressure and chip sensorsused in micro-fluidic applications.

Moreover, the sizes of the channels and of the surface etched in thesilicon are smaller, of at least one order of magnitude, than thestructure realized with the device overmolding technologies, have thephotolithographic accuracy and are compatible with the front endprocesses.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A method, comprising forming a MEMS device having a membrane sensitive to chemical or physical variations of a fluid; forming a resin layer on said membrane; removing at least a first portion of said resin layer from said membrane, so that an opening is formed over the membrane; and molding a protective casing on the MEMS device after forming the resin layer, the protective casing being in contact with the resin layer.
 2. A method according to claim 1, wherein said opening is central with respect to an active surface of the MEMS device.
 3. A method according to claim 1, wherein forming the resin layer comprises depositing the resin layer simultaneously on said membrane, on a peripheral region overlying of an active surface of the MEMS device, and on a first and a second region of said active surface that are adjacent to said membrane.
 4. A method according to claim 3, wherein said step of removing at least the first portion of said resin layer comprises etching simultaneously said resin layer from said membrane and from said peripheral region and leaving said at least one resin layer on said first and second regions.
 5. A method according to claim 1, wherein said forming the resin layer comprises depositing the resin layer limitedly on said membrane without depositing the resin layer on peripheral areas of an active surface of the MEMS device.
 6. A method according to claim 1, wherein said opening formed by removing at least the first portion of said resin layer is an opening in said resin layer.
 7. A method according to claim 1, wherein said step of removing at least the first portion of said resin layer is performed prior to molding said protective casing.
 8. A method according to claim 1, wherein said step of removing at least the first portion of said resin layer is performed after molding said protective casing.
 9. A method according to claim 1, wherein said step of forming said resin layer comprises depositing said resin layer with a spin coating technique.
 10. A method according to claim 1, wherein said step of forming said resin layer comprises depositing said resin layer with a screen printing technique.
 11. A method according to claim 1, wherein said step of forming said resin layer comprises depositing said resin layer with a stencil printing technique.
 12. A method according to claim 1, wherein said step of forming said resin layer comprises depositing said resin layer with a dispensing technique.
 13. A method according to claim 12, wherein depositing said resin layer with the dispensing technique comprises forming a resin ovoidal region.
 14. A method according to claim 13, wherein said resin ovoidal region is subjected to a curing process.
 15. A method according to claim 1, wherein said step of forming said resin layer comprises depositing said resin layer through photo-lithography.
 16. A method according to claim 1, wherein said resin layer is photo-sensitive to near-UV radiation.
 17. A method according to claim 1, wherein said resin layer is an SU-8 resin layer.
 18. A method according to claim 1, wherein said resin layer has a thickness greater than 20 μm.
 19. An electronic device comprising: a MEMS device having an active surface and a membrane, sensitive to chemical/physical variations of a fluid; first and second resin layer portions defining opposite sides of an opening over said membrane; and a protective casing surrounding the MEMS device.
 20. The device of claim 19 wherein the protective casing is positioned on top surfaces of the resin layer portions and has an opening aligned with the opening defined by the first and second resin portions.
 21. The device of claim 19 wherein the protective casing laterally surrounds the resin layer portions and leaves exposed top surfaces of the first and second resin portions.
 22. The device of claim 19 wherein the resin layer includes: a first resin layer positioned directly on the active surface of the MEMS device and having a first opening over the membrane; and a second resin layer positioned directly on the first resin layer and having a second opening aligned with the first opening.
 23. The device of claim 19 wherein the MEMS device includes a cavity underlying the membrane and an access opening allowing fluid communication between the cavity and the opening.
 24. An electronic device, comprising: a monolithic body of semiconductor material having a lower surface and an upper surface; a buried cavity extending below said upper surface and delimiting, with said upper surface, a flexible membrane; an access opening fluidically communicating with said buried cavity; a protective casing comprising an opening suitable for putting said electronic device in communication with an external fluid; a first resin layer, overlying said active surface laterally with respect to said flexible membrane, the first resin layer including first and second portions delimiting a channel region overlying said flexible membrane; and a second resin layer having a first portion and a second portion separated from each other by a space communicating below with said channel region and above with said opening of the casing, wherein said channel region communicates with said cavity through said access opening.
 25. The device of claim 24, wherein said resin layers are SU-8 resin layers.
 26. The device of claim 24, wherein said second resin layer has a thickness greater than 20 μm. 